1. Field of the Invention
The present invention relates to a digital image process field, and more particularly, to an apparatus and method for controlling a gain of a color signal applied to each pixel according to a level of the color signal by pixel of a digital image.
2. Description of the Related Art
In general, a person's vision always recognizes as having the same color on the same subject in spite of the change of a light source. That is, even in a case where a light source is changed into other light source having different color temperature like sun lights, fluorescent lamps and incandescent lamps, the person's vision always recognizes white as the same white. On the other hand, since an image sensor using a solid state imaging device is a device that converts light into an electric signal, it detects the changed color of a subject, which has a color changed according to light sources, as it is. Accordingly, most digital image processing devices (for example, digital cameras) use an algorithm for a white balance adjustment in order to represent a color detected by the image sensor similarly to the person's vision.
Generally, an auto white balance adjustment performed in the digital image processing device allows a white subject having a middle brightness level in an image to be represented in a color signal (RGB signal) having the same output level. The most general algorithm used for a relate art auto white balance adjustment adopts a scheme that calculates a color average value on the assumption of that the color average value of a screen is white regardless of the change of a light source, calculates a gain of a color signal level capable of moving the color average value to white, and applies the calculated gain to an entire image. That is, a related art auto white balance adjustment algorithm calculates and applies the gains of an R and B signals capable of correcting so that enables the R and B signals to have the same signal level as that of a G signal on a color signal (RGB signal) output from the image sensor. The related art algorithm adjusts the white balance on the basis of a gray world assumption that an integrated color is similar to an acromatic color when total color components included in an image screen are integrated.
However, the related art auto white balance adjustment algorithm adopts a scheme that performs the multiplication of the same gains on all input pixels before the correction of a gain upon correction of a color signal through the gain adjustment of the R and B signal levels. Accordingly, in a case where there exist two light sources or an emitting subject in a picture so that the picture is represented as a very bright region, the related art auto white balance adjustment algorithm corrects a color with one gain on the bright region. Therefore, a phenomenon can occur in which a color of a white region having a high brightness goes wrong, and the deflection of white balance can occur according to a level of an acromatic color region.